The present invention relates generally to the protection of electronic devices from voltage spikes and, in a preferred embodiment thereof, more particularly provides apparatus for protecting electronic devices which are powered by a vehicle's electrical system.
Quite frequently, electronic devices are installed in a vehicle by the vehicle's owner. These electronic devices may include radar detectors, stereo radios, tape decks, compact disk players, citizens band radios, cellular telephones, televisions, satellite receivers, etc. Furthermore, virtually every new vehicle manufactured today comes equipped with a multitude of electronic equipment.
Typically, one or more of these electronic devices are wired into the vehicle's electrical system so that the devices may be powered by the vehicle's battery whether or not the vehicle's engine is running. If, however, the engine is not running, the vehicle's battery is not being charged by the vehicle's charging system. This means that the vehicle's battery will be discharging if the electronic devices are operated while the vehicle's engine is not running. In addition, the vehicle's charging system may malfunction such that, even with the engine running, the vehicle's battery will be discharging while the electronic devices are being operated.
Many times these electronic devices utilize the vehicle's battery power even when they are turned off. For example, some of the electronic devices maintain data in memory chips which must remain powered to continue storing the data. Other devices have clocks, status lights, etc. which are constantly powered by the vehicle's battery. Thus, discharging of the vehicle's battery occurs even when these devices are turned off.
A few electronic devices, such as vehicle theft alarm systems, are intended to be primarily operated by the vehicle's battery when the engine is not running. In this case, the vehicle's owner will actually turn the device on when the engine is not running, knowing that the device will be operating solely on power supplied by the vehicle's battery.
On a Class 8 vehicle equipped with a satellite system and/or a sleeper unit, the satellite system will usually be left on by the vehicle's operator at all times. Additionally, the operator may fall asleep while watching television and resting in the sleeper unit during a mandatory rest period.
And finally, electronic devices are frequently left turned on by the vehicle's owner inadvertently. For example, a radar detector, typically receiving power through the vehicle's cigarette lighter receptacle, may be left on when the driver reaches a destination, turns the vehicle's engine off, and exits the vehicle. Since cigarette lighter receptacles usually remain connected to the vehicle's battery when the engine is not running, the radar detector will be discharging the battery.
The problem of vehicle battery discharging due to operation of electronic devices is compounded by the fact that large voltage spikes are created in a vehicle's electrical system when the engine is started. These voltage spikes are even larger when the vehicle's battery has been significantly discharged. Thus, electronic devices connected to the vehicle's electrical system are in danger of damage from voltage spikes when the vehicle's engine is being started, and this danger is greater when the vehicle's battery has been significantly discharged.
Solutions have been proposed to the problems associated with electronic devices discharging the vehicle's battery and being damaged when the engine is started. One solution has been to interconnect a switch between the vehicle's electrical system and an electronic device. The switch is turned off by a detecting circuit when the engine is not running. The detecting circuit senses whether or not the engine is running by monitoring the "noise" in the vehicle's electrical system which is present when the engine is running. If "noise" is present, the detecting circuit turns the switch off, thereby disconnecting the electronic device from the vehicle's electrical system.
This solution has several disadvantages, however. One disadvantage is that a switch and detecting circuit must be used for each electronic device installed in the vehicle. Another disadvantage is that "noise", a potentially harmful quality for an electronic device, is the very thing that allows the electronic device to receive power. Yet another disadvantage of this solution is that it does not solve the problem of discharge of the vehicle's battery when the engine is running.
Another solution which has been proposed is to provide a second power source, such as a second battery, exclusively for noise-sensitive electronic devices. The second battery is charged by the vehicle's normal battery when the voltage in the second battery falls below a predetermined voltage. During operation of the electronic devices, the second battery is the exclusive power source for the electronic devices.
However, this solution also has several disadvantages. One such disadvantage is that the electronic devices may completely discharge the second battery if the vehicle's engine is not running. Another disadvantage is that the operator must turn off the electronic devices in order for the second battery to be charged by the normal battery. Furthermore, the second battery may discharge the normal battery if, for example, the second battery develops a bad cell or a short therein.
Various other solutions have been proposed, each of which solve only a portion of the problems associated with powering and protecting electronic devices installed in vehicles. Unfortunately, most if not all of these solutions thereby create additional problems and inconveniences which make them undesirable.
Additionally, applicant is not aware of any existing solutions which also provide a warning to the vehicle's operator that the battery is being discharged below an acceptable level. Such a warning would be useful to the operator. It would enable the operator to turn off electronic devices and thereby conserve the remaining battery charge level. It would also signal to the operator that there may be a malfunction in the vehicle's charging circuit.
From the foregoing, it can be seen that it would be quite desirable to provide an apparatus which protects electronic devices from voltage spikes while starting a vehicle's engine, prevents discharge of the vehicle's battery whether or not the engine is running, and provides a warning to the operator that the battery is being discharged below an acceptable level. It is accordingly an object of the present invention to provide such an apparatus and associated methods of manufacturing.